In recent years, developments in displays present a development trend of high integrity and low cost. A very important technique among the developments is an implementation for mass production of GOA (Gate Driver on Array) technique. A TFT (Thin Film Transistor) gate switching circuit is integrated on an array substrate of a display panel by using the GOA technique to form a scan driving of the display panel, so that a gate driving integrate circuit part may be omitted. Thus, product cost may be reduced in terms of both material cost and manufacture process cost, and the display panel may be designed aesthetically with symmetrical sides and thin frame. Also, it benefits productivity and yield enhancement since a process for bonding in a gate direction may be omitted. The gate switching circuit integrated on the array substrate by using the GOA technique is also referred to as a GOA circuit or a shift register circuit. In a shift register circuit provided in prior art, each of shift register units includes 6 TFTs and 2 capacitors, as shown in FIG. 1, signal terminals include 3 clock signal terminals, a signal input terminal, 2 DC signal terminals (VDD (high level) terminal and VSS (low level) terminal), and an output terminal (OUTPUT). When the signal input terminal inputs a frame start signal STV and a first clock signal terminal CLK1 inputs a low level signal, a capacitor C1 holds the input frame start signal STV (low level signal), which keeps a driving transistor T8 in a turn-on state; when a second clock signal terminal CLK2 inputs the low level signal, the driving transistor T8 outputs the low level signal at the second clock signal terminal; when a third clock signal terminal CLK3 inputs the low level signal, a high voltage VDD pulls the level of the output terminal OUTPUT up and pulls the level of a node A up, such that the transistor T8 recovers to a turn-off state. The output terminal of each of shift register unit is connected to the signal input of the next shift register unit.
Since the shift register circuit is produced directly on the array substrate through a backplane process, instability in the backplane process, especially in LIPS (Low Temperature Poly-silicon) process, may result in characteristic differences among TFTs on the backplane, especially the drift of a gate threshold voltage Vth of the TFTs, which in turn causes a mal-operation of the shift register circuit. In addition, during a test for display reliability of the display product, characteristics of TFTs may change when TFTs are placed in a high-temperature high-humidity environment, which results in a Vth drift phenomena of TFTs during the operation of the shift register circuit. Therefore, the shift register circuit provided in the prior art may have a drift phenomenon in the outputted TFT gate threshold voltage Vth, which further affects the stability of output characteristics of the output terminal of the shift register circuit.